Delphi绘图功能[1] —— 入门(绘制直线和矩形)

procedure TForm1.Button1Click(Sender: TObject);
begin
    Canvas.Pen.Color := clRed;      {设置画笔颜色}
    Canvas.Pen.Width := 2;          {设置画笔宽度}
    Canvas.MoveTo(100,100);           {直线起点}
    Canvas.LineTo(500,500);         {直线起点}
    {实际上这里的Canvas是简写，也可以写做； Self.Canvas 或 Form1.Canvas}
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  Canvas.Brush.Color := clPurple;           {设置画刷颜色，也就是填充色}
  Canvas.FillRect(ClientRect);              {填充窗体客户区}
end;

unit Unit1;
interface
uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.ExtCtrls, Vcl.StdCtrls;
type
  TForm1 = class(TForm)
    Button2: TButton;
    Button3: TButton;
    Button4: TButton;
    Button5: TButton;
    Button1: TButton;
    procedure FormCreate(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
    procedure Button4Click(Sender: TObject);
    procedure Button5Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
var
  Form1: TForm1;
implementation
{$R *.dfm}
var
  btn : TButton;
//如果参数在函数中不可能修改, 一定要使用 const
const            //这里设置了不可修改的两个值
  y1 = 100;
  y2 = 500;
{在form打开时就自动创建画笔画刷}
procedure TForm1.FormCreate(Sender: TObject);
begin
  Canvas.Pen.Width := 4;
  Canvas.Pen.Color := clRed;
  Canvas.Brush.Color := clWhite;   //设置画刷颜色
end;
{1、给出左上角和右下角的坐标就可以绘制矩形}
procedure TForm1.Button1Click(Sender: TObject);
begin
   btn := TButton(Sender);
   Canvas.Rectangle(btn.Left, y1, btn.Left+btn.Width, y2);
                   { 左      上边界     右      下边界}
end;
{2、给出一个矩形结构做参数也可以绘制矩形}
procedure TForm1.Button2Click(Sender: TObject);
var
  R: TRect; {定义一个矩形结构}
begin
  btn := TButton(Sender);
  R := Rect(btn.Left, y1, btn.Left+btn.Width, y2);
  Canvas.Rectangle(R);
end;
{3、绘制圆角矩形; 前四个参数是矩形左上，右下两个点的坐标，最后两个参数是设置圆角的}
procedure TForm1.Button3Click(Sender: TObject);
begin
  btn := TButton(Sender);
  Canvas.RoundRect(btn.Left, y1, btn.Left+btn.Width, y2, 200,200);
  {最后两个参数越大，圆角弧度越大，}
end;
{4、绘制焦点矩形; 它不受画笔的影响; 它的颜色是和画刷的颜色进行某种运算得来的（与自己定义的无关）}
procedure TForm1.Button4Click(Sender: TObject);
var
  R: TRect;
begin
  btn := TButton(Sender);
  R := Rect(btn.Left, y1, btn.Left+btn.Width, y2);
  Canvas.DrawFocusRect(R);         //获得焦点显示/隐藏
end;
{5、矩形描边, 用的不是画笔是画刷}
procedure TForm1.Button5Click(Sender: TObject);
var
  R: TRect;
begin
  btn := TButton(Sender);
  R := Rect(btn.Left, y1, btn.Left+btn.Width, y2);
  Canvas.FrameRect(R);
end;
end.